Sigma-delta modulators provide excellent analog-to-digital, digital-to-analog, and digital-to-digital conversion capabilities in an economical and efficient manner. One significant advantage of a sigma-delta modulator is that a high resolution input signal can be converted to a lower resolution signal using only a limited resolution quantizer. Unfortunately, high resolution can only be maintained for low and medium signal bandwidths. As such, sigma-delta modulators are mainly incorporated in devices where the bandwidth of the input signal is small relative to the operating rate of the sigma-delta modulator. Sigma-delta modulators are often found in audio applications and the like. The bandwidth restriction associated with sigma-delta modulators is indirectly due to the feedback path within a typical sigma-delta modulator architecture. Providing the feedback and the necessary processing associated therewith significantly limits the operating rate of the sigma-delta modulator. The restricted operating range corresponds to restricted bandwidths.
Normally, sigma-delta modulators are not used in wideband wireless applications, such as those requiring digital-to-analog conversion. Wideband wireless transmitters often incorporate lower speed digital-to-analog converters followed by an analog upconversion process and a conventional power amplifier. This traditional approach suffers from the normal limitations associated with analog circuitry, including component variations and temperature stability. The simplicity and cost effectiveness of sigma-delta modulators would be beneficial in wideband wireless applications to overcome these limitations; however, the large signal bandwidths and the high carrier frequencies have made sigma-delta modulators impractical.
Accordingly, there is a need for a way to incorporate sigma-delta modulators in wideband wireless applications and in other high-frequency applications in a cost-effective and efficient manner, while overcoming the traditional bandwidth limitations associated with sigma-delta modulators.